Medium for the specific detection of resistant microorganisms

ABSTRACT

A method for distinguishing among a first group of microorganisms belonging to a first taxon of Gram negative bacteria, the first group of bacteria exhibiting a mechanism of resistance to a treatment; a second group of microorganisms belonging to a second taxon of Gram negative bacteria, the second taxon of bacteria being different than said first taxon, and exhibiting a mechanism of resistance to a treatment identical to the mechanism of the first group; and a third group of Gram negative bacteria that is not resistant to the treatment.

CROSS-REFERENCE TO PRIOR APPLICATIONS

This is a divisional of application Ser. No. 11/794,907 filed Jul. 9, 2007, which is a National Stage Application of PCT/FR2006/050109 filed Feb. 9, 2006, and claims the benefit of French Application Nos. 0550394 filed Feb. 10, 2005 and 0553049 filed Oct. 7, 2005. The entire disclosures of the prior applications are hereby incorporated by reference herein in their entirety.

The field of the invention is that of microbiological analysis by means of biochemistry, and in particular the detection and identification of microorganisms, for instance of bacteria or yeasts.

Bacterial resistance to antibiotics is a major public health problem. The resistance of infectious microorganisms to a treatment has developed at the same time as anti-infectious molecules and today represents a major obstacle in therapeutics. This resistance is responsible for many problems, including difficulties in detection in the laboratory, limited treatment options and a deleterious impact on clinical outcome.

In particular, the rapid and irrepressible increase in the resistance of pathogenic bacteria, over the last 20 years, represents one of the major current problems in medicine. Infections caused by these organisms are responsible for extended periods of hospitalization and are associated with high morbidity and mortality rates, following therapeutic failures.

Several resistance mechanisms can be involved simultaneously in a bacterial strain. They are generally classified in 3 categories: deficient penetration of the antibiotic into the bacterium, inactivation or excretion of the antibiotic by bacterial enzymatic systems, and lack of affinity between the bacterial target and the antibiotic.

Enzymatic inactivation is the most common mechanism of acquired resistance in terms of number of species and of antibiotics involved. Thus, chromosomal class C cephalosporinases today constitute one of the predominant resistance mechanisms of gram-negative bacteria, the bacteria expressing such enzymes being resistant to cephalosporins. Similarly, β-lactamases are enzymes expressed by certain bacteria, capable of hydrolyzing the C—N bond of the β-lactame ring, the basic structure of antibiotics of the β-lactamine family, so as to give a microbiologically inactive product. Several β-lactamase inhibitors (BLIs), such as clavulanic acid (CA), tazobactam and sulbactam, have been developed in order to increase the antimicrobial activity and broaden the spectrum of the β-lactamines which are associated therewith. They act as a suicide subject for β-lactamases, and prevent enzymatic degradation of the antibiotics and allow them to become effective against bacteria that were initially resistant. However, by virtue of the persistent exposure of strains to antibiotic pressure, the bacteria express their ability to adapt through the continuous and dynamic production of β-lactamases, which evolves at the same time as the development of new molecules.

Gram-negative bacteria which produce high-level chromosome class C cephalosporinases (reference is made to HL Case bacteria), and also gram-negative bacteria which produce extended-spectrum β-lactamase (reference is then made to ESBL bacteria) have, as a result, become an increasing threat, in particular because the number of bacterial species concerned is increasing. HL Case and ESBL bacteria are resistant to treatments based on 1st- and 2nd-generation penicillins and cephalosporines, but also on 3rd-generation cephalosporines (C3G) (cefotaxim CTX, ceftazidime CAZ, cefpodoxime CPD, ceftriaxone CRO) and monobactams (aztreonam ATM). On the other hand, 7α-methoxycephalosporins (cephamycins: cefoxitin, cefotetan) and carbapenems (imipenem, meropenem, ertapenem) generally conserve their activity. ESBLs are inhibited by β-lactamase inhibitors (BLIs), which makes it possible to differentiate them from other cephalosporinases.

These bacteria thus most commonly simultaneously express resistances to several treatments, which poses difficulties in setting up a relevant treatment and avoiding therapeutic failures. An Escherichia coli bacterium can thus be HL Case and ESBL. In addition, since ESBL-positive enterobacteria have a tendency to disseminate the resistance by clonal transmission of strains or conjugative plasma transfer, they represent a problem in terms of controlling infections. In most studies, Escherichia coli and Klebsiella pneumoniae remain the most common ESBL-producing species. However, over the last few years, ESBLs have greatly broadened their panel of host species. In fact, many species of enterobacteria and of nonfermenting gram-negative bacilli (such as Pseudomonas aeruginosa) have also been reported to ESBL producers.

In addition to these ESBL bacteria, mention may also be made of Staphylococcus aureus bacteria, which are also pathogenic bacteria that develop many mechanisms of resistance, such as resistance to methicillin, penicillin, tetracycline, erythromycin, or vancomycin. Enterococcus faecium is another multiresistant bacterium found in the hospital environment, which can be resistant to penicillin, vancomycin and linezolide. Mycobacterium tuberculosis is commonly resistant to isoniazid and to rifampicin. Other pathogens offer certain resistances, such as Salmonella, Campylobacter and Streptococcus.

It therefore becomes essential, from a public health point of view, to be able to identify such microorganisms, and such resistance mechanisms, as rapidly as possible.

In general, the search for microorganisms resistant to a treatment is carried out according to the following steps:

1. Taking a biological sample that may contain said microorganisms;

2. Seeding and incubating a culture medium (18 to 48 h) in order to induce exponential growth of the microorganisms;

3. Pinpointing, on the culture media, colonies of potentially significant microorganisms;

4. Characterizing the microorganism species;

5. Identifying the mechanisms of resistance of the microorganisms analyzed, their biological significance and, optionally, the appropriate therapy.

This succession of steps involves a considerable amount of time between taking the sample that may contain microorganisms and prescribing a treatment that is appropriate for the patient. Furthermore, the user must generally perform steps for transferring microorganims from a first medium to a second medium manually, which can induce problems, in particular, of contamination, but also risks to the handler's health.

By way of example, in order to detect the presence of broad-spectrum beta-lactamases (ESBLs) in strains of Escherichia coli and Klebsiella pneumoniae, use may be made of a diffusion technique as described in the publication by Jacoby & Han (J Clin Microbial. 34(4): 908-11, 1996), which does not however give any information regarding the identification of the strains tested: it is possible to determine whether or not the bacterium is a ESBL-producing bacterium, but it is not possible to distinguish whether such a bacterium is an Escherichia coli or a Klebsiella pneumoniae.

Metabolic substrates are also used for detecting the presence of ESBLs or HL cases. In this respect, AES laboratories proposes a medium in a biplate combining a Drigalski medium with cefotaxim and a MacConkey medium with ceftazidime. The Drigalski and MacConkey media make it possible to reveal lactose acidification, a metabolism which is present in a very large number of enterobacterial species. However, such a medium only makes it possible to distinguish resistant bacteria from non-resistant bacteria, and does not make it possible to distinguish bacteria expressing a ESBL from those expressing an HL Case. Neither does this medium make it possible to identify specific bacterial species, nor does it make it possible, for example, to discriminate between E. coli bacteria and K. pneumoniae bacteria.

In the case of the detection of resistance mechanisms other than ESBL, mention may be made of patent application EP0954560, which relates to the search for Vancomycin-resistant enterococcal, by combining Vancomycin with a chromogenic media that reveals two enzymatic activities (β-glucosidase and pyrrolidonyl arylamidase). However, this chromogenic medium makes it possible to determine only whether or not the vancomycin-resistant strains belong to the Enterococcus genus, but does not make it possible to identify the species or the resistance mechanisms involved, in particular if it is a question of an acquired or wild-type resistance.

Thus, the characterization of a species of microorganism, and then the identification of its resistance to a treatment, is long and laborious. If the laboratory gives the clinician a positive screen, whereas the isolate is in fact free of resistant microorganisms, this can lead to needless and inappropriate treatment. Conversely, not communicating a positive screen, which is subsequently confirmed, delays the setting of the isolation of the patient (and possibly an appropriate therapy) by one day. This shows the need for a rapid and reliable confirmation test.

The present invention therefore proposes to improve the prior art by providing a novel diagnostic tool which allows a gain in time, in reliability and in relevance with respect to the therapy implemented. Our invention makes it possible, in a single step, to identify the species of microorganisms present in a sample, and to determine their mechanism of resistance in order to propose a treatment appropriate to each patient. This invention is particularly suitable for discriminating various species of microorganisms, which have various mechanisms of resistance to various treatments, but all of which may be present in the same sample.

Before going any further in the disclosure of the invention, the following definitions are given in order to facilitate understanding of the invention:

The term “culture medium” is intended to mean a medium comprising all the elements required for the survival and/or the growth of microorganisms. The culture medium according to the invention may contain any possible additives, for instance: peptones, one or more growth factors, carbohydrates, one or more selective agents, buffers, one or more gelling agents, etc. This culture medium may be in liquid form or in gel form which is ready to use, i.e. ready for seeding in a tube or flask or on a Petri plate.

For the purpose of the present invention, the term “microorganism” covers gram-positive or gram-negative bacteria, yeasts and, more generally, organisms that are generally unicellular, invisible to the naked eye, which can be multiplied and handled in the laboratory.

By way of gram-negative bacteria, mention may be made of bacteria of the following genres: Pseudomonas, Escherichia, Salmonella, Shigella, Enterobacter, Klebsiella, Serratia, Proteus, Campylobacter, Haemophilus, Morganella, Vibrio, Yersinia, Acinetobacter, Branhamella, Neisseria, Burkholderia, Citrobacter, Hafnia, Edwardsiella, Aeromonas, Moraxella, Pasteurella, Providencia, and Legionella.

By way of gram-positive bacteria, mention may be made of bacteria of the following genre: Enterococcus, Streptococcus, Staphylococcus, Bacillus, Listeria, Clostridium, Gardnerella, Kocuria, Lactococcus, Leuconostoc, Micrococcus, Mycobacteria and Corynebacteria.

By way of yeasts, mention may be made of yeasts of the following genre: Candida, Cryptococcus, Saccharomyces and Trichosporon.

The term “biological sample” is intended to mean a clinical sample, derived from a specimen of biological fluid, or a food sample, derived from any type of food. This sample may thus be liquid or solid and mention may be made, in the nonlimiting manner, of a clinical blood, plasma, urine or faeces sample, nose, throat, skin, wound or cephalospinal fluid specimens, a food sample from water, from drinks such as milk or a fruit juice; from yoghurt, from meat, from eggs, from vegetables, from mayonnaise, from cheese; from fish, etc., a food sample derived from a feed intended for animals, such as, in particular, a sample derived from animal meals.

The term “mechanism of resistance” is intended to mean any type of device which allows a microorganism to render a treatment partially or completely ineffective on said microorganism, guaranteeing its survival. The mechanisms of resistance are generally divided up into three categories: deficient penetration of the antibiotic into the bacterium, inactivation or excretion of the antibiotic by means of bacterial enzymatic systems, and lack of affinity between the bacterial target and the antibiotic.

By way of indication, mention may in particular be made of mechanisms of resistance related to the expression of an enzyme belonging to the broad-spectrum β-lactamase group; of an enzyme belonging to the chromosomal high level class C cephalosporinase group; mechanisms of resistance to glycopeptides, preferably developed by bacteria belonging to the Enterococcus genus.

Mention will also be made of mechanisms of resistance to methicillin, penicillin, tetracycline, erythromycin, or vancomycin when the microorganism is a Staphylococcus aureus bacterium.

Mention will also be made of mechanisms of resistance to penicillin, vancomycin and linezolide when the microorganism is an Enterococcus faecium bacterium.

Mention will also be made of mechanisms of resistance to amphotericin B or to antifungals of the azole family when the microorganism is a yeast.

Finally, mention will be made of mechanisms of resistance to isoniazid and to rifampicin when the microorganism is a Mycobacterium tuberculosis bacterium.

The term “treatment” is intended to mean a treatment capable of preventing or reducing the growth of microorganisms derived from a patient. This treatment may comprise in particular antimicrobial compounds, such as antibiotics, for instance penicillins, conventional cephalosporins, broad-spectrum cephalosporins, monobactams, glycopeptides or aminosides, or such as antifungals or resistance-inhibiting compounds. It should be noted that this treatment can also comprise the isolation of the patient, thereby preventing propagation of the microorganism among other patients.

The term “substrate” which allows the detection of an enzymatic or metabolic activity is intended to mean any molecule capable of directing or indirectly generating a detectable signal due to an enzymatic or metabolic activity of the microorganism.

When this activity is an enzymatic activity, reference is then made to an enzymatic substrate. The term “enzymatic substrate” is intended to mean any substrate that can be hydrolyzed by an enzyme into a product that allows the direct or indirect detection of a microorganism. This substrate comprises in particular a first part that is specific for the enzymatic activity to be revealed and a second part that acts as a label, hereinafter referred to as labeling part. This labeling part may be chromogenic, fluorogenic, luminescent, etc. As chromogenic substrate suitable for solid supports (filter, agar, electrophoresis gel), mention may in particular be made of substrates based on indoxyl and its derivatives, and substrates based on hydroxyquinoline or escultin and their derivatives, which allow the detection of osidase and esterase activities. Mention may also be made of substrates based on nitrophenol and nitroaniline and derivatives, making it possible to detect osidase and esterase activities in the case of substrates based on nitrophenol, and peptidase activities in the case of substrates based on nitroaniline. Finally, mention may be made of substrates based on naphtol and naphtylamine and their derivatives, which make it possible to detect osidase and esterase activities via naphtol, and peptidase activities via naphtylamine. This substrate may allow, in particular, but in a nonlimiting manner, the detection of an enzymatic activity such as the activity of an osidase, peptidase, esterase, etc. The enzymatic substrate can also be a natural substrate of which the product of hydrolysis is detected directly or indirectly. As natural substrate, mention may in particular be made of tryptophan for detecting tryptophanase or desaminase activity, a cyclic amino acid (tryptophan, phenylalanine, histidine, tyrosine) for detecting desaminase activity, phosphatidyl inositol for detecting phospholipase activity, etc.

When this activity is a metabolic activity, the substrate is then a metabolic substrate, such as a source of carbon or of nitrogen, coupled to an indicator that produces a coloration in the presence of one of the metabolic products.

According to a preferred embodiment of the invention, said first and/or second enzymatic or metabolic activity is an enzymatic activity preferably chosen from the enzymatic activities: beta-glucosidase, desaminase, beta-glucuronidase, beta-galactosidase, alpha-glucosidase, alpha-galactosidase, hexosaminidase, N-acetyl-hexosaminidase, phosphatase, esterase, and aminopeptidase.

For example, for detecting E. coli, use is preferably made of beta-glucuronidase or β-galactosidase or tryptophanase or desaminase activity; for detecting Proteus, use is preferably made of desaminase activity; for detecting enterococci, use is preferably made of beta-glucosidase activity. For Candida albicans, hexosaminidase is preferred, for Listeria monocytogenes, phospholipase is preferred, for salmonellae, esterase is preferred, for Pseudomonas aeruginosa, esterase or β-alanine aminopeptidase is preferred, for Staphylococcus aureus phosphatase or alpha-glucosidase is preferred.

The expression “marker for differentiating” two groups of microorganisms is intended to mean a compound which does not have the same properties on a first and on a second group. This compound may thus be:

-   -   a specific substrate;     -   an inhibitor of a mechanism of resistance, which then makes it         possible to inhibit the growth of the organisms developing a         specific resistance, without any discrimination of the         microorganism species.

In the case of the use of a specific substrate, use is preferably made of beta-glucuronidase, beta-galactosidase, tryptophanase or desaminase activity for detecting E. coli, use is preferably made of desaminase activity for detecting Proteus,

use is preferably made of beta-glucosidase activity for detecting enterococci. For Candida albicans, hexosaminidase is preferred, for Listeria monocytogenes, phospholipase is preferred, for salmonellae,

esterase is preferred, for Pseudomonas aeruginosa, esterase or β-alanine aminopeptidase is preferred, for Staphylococcus aureus, phosphatase or alpha-glucosidase is preferred.

In the case of the use of an inhibitor of a mechanism of resistance, use is preferably made of:

-   -   clavulanic acid, tazobactam or sulbactam when the first group         and/or the second group comprises a mechanism of resistance         induced by an expression of β-lactamases. The clavulanic acid         concentration in the medium is then preferably between 0.05 and         32 mg/l, preferably between 0.1 and 8 mg/l, and even more         preferably between 0.25 and 6 mg/l;     -   cloxacillin or dicloxacillin when the first group and/or the         second group comprises a mechanism of resistance induced by the         expression of cephalosporinases.

The term “taxon” is intended to mean a group of microorganisms having a taxonomic unit. A taxon may be a family, a genus, a set of genre, a species, a set of species or a subspecies. By way of indication, mention may be made of enterobacteria, Klebsiella, Escherichia, Enterobacter, Citrobacter, Serratia, KESC (Klebsiella, Enterobacter, Serratia, Citrobacter), Proteeae, Proteus, Morganella, Pseudomonas, Staphylococcus, Streptococcus, Enterococcus, Candida, Escherichia coli, Escherichia coli O157:H7, Klebsiella pneumoniae, Citrobacter freundii, Enterococcus faecalis, Enterococcus faecium, Staphylococcus aureus, coagulase-negative staphylocoque, Candida albicans, Candida glabrata, Candida krusei, Candida lusitaniae.

The term “antimicrobial” is intended to mean any compound capable of preventing or slowing down the growth of a microorganism. This compound may be an antibiotic or an antifungal.

The term “antibiotic” is intended to mean any compound capable of preventing or slowing down the growth of a bacterium. By way of indication, mention may in particular be made of the antibiotics cefotaxime, ceftazidime, ceftriaxone, cefpodoxime, aztreonam, vancomycin, tobramycin and ciprofloxacin.

The term “antifungal” is intended to mean any compound capable of preventing or slowing down the growth of a yeast or of a mould. By way of indication, mention may in particular be made of amphotericin B, fluconazole, itraconazole, voriconazole and cycloheximide.

According to a preferred embodiment of the invention, when the antibiotic is

-   -   cefotaxime, the cefotaxime concentration in the medium is         preferably between 0.25 and 8 mg/l, preferably between 1 and 2         mg/l;     -   ceftazidime, the ceftazidime concentration in the medium is         preferably between 0.25 and 8 mg/l, preferably between 2 and 2.5         mg/l;     -   ceftriaxone, the ceftriaxone concentration in the medium is         preferably between 0.25 and 8 mg/l, preferably between 1 and 2.5         mg/l;     -   cefpodoxime, the cefpodoxime concentration in the medium is         preferably between 0.1 and 32 mg/l, preferably between 0.75 and         10 mg/l, and even more preferably between 1 and 6 mg/l;     -   aztreonam, the aztreonam concentration in the medium is         preferably between 0.1 and 8 mg/l, preferably between 0.75 and         1.5 mg/l.

According to a specific embodiment of the invention, the medium comprises a combination of at least two antibiotics. Preferably, the combination of at least two antibiotics comprises cefotaxime and ceftazidime.

Irrespective of the embodiment of the invention, the medium may also comprise a dye. By way of indication of a dye, mention may be made of Evans blue, neutral red, sheep blood, horse blood, and opacifier such as titanium oxide, nitroaniline, malachite green, brilliant green, etc.

All the media may also comprise, in order to increase their sensitivity:

-   -   at least one antimicrobial that is active against gram-positive         bacteria, such as in particular linezolide or vancomycin;     -   at least one antimicrobial that is active against yeasts, such         as in particular voriconazole or amphotericin B.

In this respect, the invention relates to the use of a combination of two culture media for distinguishing at least three groups of microorganisms in a biological sample, comprising:

-   -   a first group of microorganisms, belonging to a first taxon of         microorganisms and comprising at least a first mechanism of         resistance to a first treatment;     -   a second group of microorganisms, belonging to a second taxon of         microorganisms and comprising at least a second mechanism of         resistance to a second treatment;     -   a third group of microorganisms, that are not resistant to said         first and second treatments,

said combination of two culture media comprising:

-   -   a. at least a first substrate for detecting at least a first         enzymatic or metabolic activity of said first group of         microorganisms;     -   b. at least two markers for differentiating the first group of         microorganisms and the second group of microorganisms;     -   c. at least one antimicrobial that is active on said third group         of microorganisms.

Preferably, the medium comprises at least two markers for differentiating the first group of microorganisms and the second group of microorganisms, at least one of which is an inhibitor of said first or said second mechanism of resistance. The medium may also comprise at least two markers for differentiating the first group of microorganisms and the second group of microorganisms, which are each an inhibitor of said first or said second mechanism of resistance.

This first embodiment of the invention makes it possible to distinguish, in the same sample, a first and a second group comprising various species or various taxons of microorganisms, each of the two groups being resistant to a different treatment.

This embodiment of the invention thus makes it possible, for example, to distinguish, in the same sample, a first group comprising E. coli ESBL bacteria and a second group comprising KESC HL Case bacteria. In this specific case, the combination of two media may be the following:

-   -   At least a first substrate which makes it possible to         identify E. coli bacteria, for example a glucuronidase         substrate, such as 6-chloro-3-indolyl-β-D-glucuronide, or a         galactosidase substrate, such as         5-bromo-6-chloro-3-indolyl-β-D-galactoside;     -   a first identification marker which is a glucosidase substrate,         such as 5-bromo-4-chloro-3-indolyl-β-D-glucoside, which makes it         possible to identify KESC bacteria;     -   a second identification marker which is a resistance mechanism         inhibitor, such as cloxacillin;     -   at least one antimicrobial which is an antibiotic, such as         cefpodoxime.

Reference is made to a combination of 2 media, i.e. a first medium may comprise:

-   -   a first substrate which makes it possible to identify E. coli,         for example a glucuronidase substrate, such as         6-chloro-3-indolyl-β-D-glucuronide or a galactosidase substrate,         such as 5-bromo-6-chloro-3-indolyl-β-D-galactoside;     -   a first marker which is a resistance mechanism inhibitor, such         as cloxacillin;     -   an antimicrobial which is an antibiotic, such as cefpodoxime,

or the second medium comprises:

-   -   a first substrate which makes it possible to identify E. coli,         for example a glucuronidase substrate, such as         6-chloro-3-indolyl-β-D-glucuronide, or a galactosidase         substrate, such as 5-bromo-6-chloro-3-indolyl-β-D-galactoside;     -   a first marker which is a glucosidase substrate, such as         5-bromo-4-chloro-3-indolyl-β-D-glucoside, which makes it         possible to identify KESC bacteria;     -   an antimicrobial which is an antibiotic, such as ceftazidime.

Another alternative would be to use a first medium comprising:

-   -   a first substrate which makes it possible to identify E. coli,         for example a glucuronidase substrate, such as         6-chloro-3-indolyl-β-D-glucuronide, or a galactosidase         substrate, such as 5-bromo-6-chloro-3-indolyl-β-D-galactoside;     -   a first marker which is a glucosidase substrate, such as         5-bromo-4-chloro-3-indolyl-β-D-glucoside, which makes it         possible to identify KESC bacteria;     -   an antimicrobial which is an antibiotic, such as aztreonam,

while the second medium comprises:

-   -   a first substrate which makes it possible to identify E. coli,         for example a glucuronidase substrate, such as         6-chloro-3-indolyl-β-D-glucuronide, or a galactosidase         substrate, such as 5-bromo-6-chloro-3-indolyl-β-D-galactoside;     -   a first marker which is a resistance mechanism inhibitor, such         as clavulanic acid;     -   an antimicrobial which is an antibiotic, such as ceftazidime.

Those skilled in the art will choose each medium so as to systematically obtain a combination according to the invention. The antimicrobial that is active on said third group is present in the two media. Those skilled in the art may in particular use a biplate, for readily comparing the two media on which the same biological sample has been deposited.

In this respect, the invention also relates to a biplate comprising a combination of two culture media, said combination comprising:

-   -   a. at least a first substrate for detecting at least a first         enzymatic or metabolic activity of said first group of         microorganisms;     -   b. at least two markers for differentiating the first group of         microorganisms and the second group of microorganisms;     -   c. at least one antimicrobial that is active on said third group         of microorganisms, said antimicrobial being present on each side         of the biplate.

This first embodiment of the invention is not limited to distinguishing between 3 groups of microorganisms, but may make it possible to distinguish between 4, 5 or even more groups of microorganisms. It is then necessary to add additional identification markers to the medium or media, in order to discriminate between the various groups.

In this respect, the invention also relates to a biplate comprising a combination of two culture media, said combination comprising:

for the first medium:

-   -   a first substrate which makes it possible to identify E. coli,         for example a glucuronidase substrate such as         6-chloro-3-indolyl-β-D-glucuronide, or a galactosidase         substrate, such as 5-bromo-6-chloro-3-indolyl-β-D-galactoside,         or a substrate which makes it possible to identify Proteeae, for         example tryptophan;     -   a first identification marker which is a glucosidase substrate,         such as 5-bromo-4-chloro-3-indolyl-β-D-glucoside;     -   a second identification marker which is a resistance inhibitor,         such as cloxacillin;     -   at least one antimicrobial which is an antibiotic, such as         cefpodoxime;

for the second medium:

-   -   a first substrate which makes it possible to identify         enterococci, for example a glucosidase substrate, such as         5-bromo-4-chloro-3-indolyl-β-D-glucoside;     -   a first identification marker which is another glucosidase         substrate, such as methyl-α-glucoside;     -   at least one antimicrobial which is an antibiotic, such as         vancomycin.

The invention also relates to the use of a culture medium for distinguishing at least 3 groups of microorganisms in a biological sample, comprising:

-   -   a first group of microorganisms, belonging to a first taxon of         microorganisms and comprising at least one mechanism of         resistance to a treatment;     -   a second group of microorganisms, belonging to a second taxon of         microorganisms, different than said first taxon, but comprising         at least one mechanism of resistance to a treatment, identical         to that of the first group;     -   a third group of microorganisms, that are not resistant to said         treatment, said culture medium comprising:         -   a. at least a first substrate for detecting at least a first             enzymatic or metabolic activity of said first group of             microorganisms;         -   b. at least one marker for differentiating the first group             of microorganisms and the second group of microorganisms,             said marker being a substrate for detecting at least one             enzymatic or metabolic activity of said second group of             microorganisms;         -   c. at least one antimicrobial that is active on said third             group of microorganisms.

This second embodiment of the invention makes it possible to distinguish, in the same sample, a first and a second group comprising various species or various taxons of microorganisms, but each of the two groups being resistant to the same treatment. In this specific embodiment of the invention, it is not necessary to use a combination of media, since a single medium comprising the characteristics as defined above is sufficient.

This embodiment of the invention thus makes it possible, for example, to distinguish, in the same sample, a first group comprising E. coli ESBL bacteria and a second group comprising KESC ESBL bacteria.

In this respect, the invention relates to a culture medium comprising:

-   -   a first substrate for detecting a beta-glucosidase enzymatic         activity, preferably 5-bromo-4-chloro-3-indolyl-β-D-glucoside,         at a concentration of between 25 and 500 mg/l, preferably         between 40 and 150 mg/l;     -   a second substrate for detecting methyl-alpha-glucoside         metabolism, in the presence of a colored indicator, preferably         neutral red, at a concentration of between 2 and 100 mg/l,         preferably between 4 and 50 mg/l;     -   an antimicrobial which is an antibiotic, preferably vancomycin,         at a concentration of between 0.5 and 128 mg/l, preferably         between 2 and 32 mg/l.

When the antibiotic is vancomycin, this medium is preferably used for distinguishing:

-   -   a first group of enterococcal bacteria developing an acquired         resistance against vancomycin;     -   a second group of enterococcal bacteria developing a natural         resistance against vancomycin;     -   a third group of enterococcal bacteria that are not resistant to         vancomycin.

The invention also relates to a culture medium comprising:

-   -   a first substrate for detecting a hexosaminidase enzymatic         activity, preferably         5-bromo-4-chloro-3-indolyl-N-acetyl-β-D-glucosaminide, and a         concentration between 25 and 500 mg/l, preferably between 40 and         150 mg/l;     -   a second substrate for detecting a beta-glucosidase activity,         preferably 6-chloro-3-indolyl-β-D-glucoside, at a concentration         of between 25 and 500 mg/l, preferably between 40 and 200 mg/l;     -   an antimicrobial which is an antifungal, which is preferably         amphotericin B (amphoB), at a concentration of between 0.5 and         64 mg/l, preferably between 1 and 16 mg/l, even more preferably         between 1 and 8 mg/l.

When the antifungal is amphotericin B, this medium is preferably used to distinguish:

-   -   a first group of yeasts comprising Candida albicans developing a         resistance to amphoB;     -   a second group of yeasts comprising Candida tropicalis and/or C.         lusitaniae and/or C. kefyr, developing a resistance to amphoB;     -   a third group of yeasts that are not resistant to amphoB.

The invention also relates to a culture medium comprising:

-   -   a first substrate for detecting a hexosaminidase enzymatic         activity, preferably         5-bromo-4-chloro-3-indolyl-N-acetyl-β-D-glucosaminide, at a         concentration of between 25 and 500 mg/l, preferably between 40         and 150 mg/l;     -   a second substrate for detecting a phosphatase activity,         preferably 5-bromo-6-chloro-3-indolylphosphate, at a         concentration of between 25 and 750 mg/l, preferably between 40         and 200 mg/l;     -   an antimicrobial which is an antifungal, which is preferably         amphoB, at a concentration of between 0.5 and 64 mg/l,         preferably between 1 and 16 mg/l, even more preferably between 1         and 8 mg/l.

When the antifungal is amphotericin B, this medium is preferably used to distinguish:

-   -   a first group of yeasts comprising Candida albicans developing a         resistance to amphoB;     -   a second group of yeasts comprising Candida tropicalis and/or C.         glabrata and/or C. krusei, developing a resistance to amphoB;     -   a third group of yeasts that are not resistant to amphoB.

The invention also relates to a culture medium comprising:

-   -   a first substrate for detecting the hexosaminidase enzymatic         activity of said first group, preferably         5-bromo-4-chloro-3-indolyl-N-acetyl-β-D-glucosaminide, at a         concentration of between 25 and 500 mg/l, preferably of between         40 and 150 mg/l;     -   a second substrate for detecting the beta-glucosidase activity         of said second group, preferably         6-chloro-3-indolyl-β-D-glucoside, at a concentration of between         25 and 500 mg/l, preferably between 40 and 200 mg/l;     -   an antimicrobial which is an antifungal, preferably fluconazole,         at a concentration of between 1 and 256 mg/l, preferably between         2 and 128 mg/l, even more preferably between 8 and 64 mg/l.

When the antifungal is fluconazole, this medium is preferably used to distinguish:

-   -   a first group of yeasts comprising Candida albicans developing a         resistance to fluconazole;     -   a second group of yeasts, comprising Candida tropicalis         and/or C. lusitaniae and/or C. kefyr, developing a resistance to         fluconazole;     -   a third group of yeasts that are not resistant to fluconazole.

The invention also relates to a culture medium comprising:

-   -   a first substrate for detecting a hexosaminidase enzymatic         activity, preferably         5-bromo-4-chloro-3-indolyl-N-acetyl-β-D-glucosaminide, at a         concentration of between 25 and 500 mg/l, preferably between 40         and 150 mg/l;     -   a second substrate for detecting a phosphatase activity,         preferably 5-bromo-6-chloro-3-indolylphosphate, at a         concentration of between 25 and 750 mg/l, preferably between 40         and 200 mg/l;     -   an antimicrobial which is an antifungal, which is preferably         fluconazole, at a concentration of between 1 and 256 mg/l,         preferably between 2 and 128 mg/l, even more preferably between         8 and 64 mg/l.

When the antifungal is fluconazole, this medium is preferably used to distinguish:

-   -   a first group of yeasts comprising Candida albicans developing a         resistance to fluconazole;     -   a second group of yeasts, comprising Candida tropicalis         and/or C. glabrata and/or C. krusei, developing a resistance to         fluconazole;     -   a third group of yeasts that are not resistant to fluconazole.

The invention also relates to a culture medium comprising:

-   -   a first substrate for detecting a beta-glucuronidase enzymatic         activity, preferably 6-chloro-3-indolyl-β-D-glucuronide, at a         concentration of between 25 and 750 mg/l, preferably between 40         and 300 mg/l, or a beta-galactosidase enzymatic activity,         preferably 5-bromo-6-chloro-3-indolyl-β-D-galactoside, at a         concentration of between 25 and 500 mg/l, preferably between 40         and 150 mg/l;     -   a second substrate for detecting a beta-glucosidase activity,         preferably 5-bromo-4-chloro-3-indolyl-β-D-glucoside, at a         concentration of between 25 and 500 mg/l, preferably between 40         and 250 mg/l, or a tryptophanase or desaminase activity,         preferably tryptophan, at a concentration of between 50 and 5000         mg/l, preferably between 250 and 2000 mg/l;     -   an antimicrobial which is an antibiotic, preferably ceftazidime.         The ceftazidime concentration in the medium is then preferably         between 0.25 and 8 mg/l, preferably between 2 and 2.5 mg/l.

When the antibiotic is ceftazidime, this medium is preferably used to distinguish:

-   -   a first group of E. coli ESBL or HL Case bacteria;     -   a second group of KESC ESBL or HL Case bacteria;     -   a third group of bacteria that are not resistant to         beta-lactamines and to cephalosporins.

The invention also relates to a culture medium comprising:

-   -   a first substrate for detecting a beta-glucuronidase or         beta-galactosidase enzymatic activity, preferably         6-chloro-3-indolyl-β-D-glucuronide, at a concentration of         between 25 and 750 mg/l, preferably between 40 and 300 mg/l, or         5-bromo-6-chloro-3-indolyl-β-D-galactoside, at a concentration         of between 25 and 500 mg/l, preferably between 40 and 150 mg/l;     -   a second substrate for detecting a beta-glucosidase activity,         preferably 5-bromo-4-chloro-3-indolyl-β-D-glucoside, at a         concentration of between 25 and 500 mg/l, preferably between 40         and 250 mg/l, or a tryptophanase or desaminase activity,         preferably tryptophan, at a concentration of between 50 and 5000         mg/l, preferably between 250 and 2000 mg/l;     -   an antimicrobial which is an antibiotic, preferably cefpodoxime,         at a concentration of between 0.5 and 32 mg/l, preferably         between 0.75 and 10 mg/l, and even more preferably between 1 and         6 mg/l, and cloxacillin, at a concentration of between 10 and         2000 mg/l, preferably between 50 and 500 mg/l.

When the antibiotic is cefpodoxime, this medium is preferably used to distinguish:

-   -   a first group of E. coli ESBL bacteria;     -   a second group of KESC ESBL bacteria;     -   a third group of bacteria that are not resistant to         beta-lactamines.

The invention also relates to a culture medium comprising:

-   -   a first substrate for detecting a beta-glucuronidase enzymatic         activity, preferably 6-chloro-3-indolyl-β-D-glucuronide, at a         concentration of between 25 and 750 mg/l, preferably between 40         and 300 mg/l, or a beta-galactosidase enzymatic activity,         preferably 5-bromo-6-chloro-3-indolyl-β-D-galactoside, at a         concentration of between 25 and 500 mg/l, preferably between 40         and 150 mg/l;     -   a second substrate for detecting a beta-glucosidase activity,         preferably 5-bromo-4-chloro-3-indolyl-β-D-glucoside, at a         concentration of between 25 and 500 mg/l, preferably between 40         and 250 mg/l, or a tryptophanase or desaminase activity,         preferably tryptophan, at a concentration of between 50 and 5000         mg/l, preferably between 250 and 2000 mg/l;     -   a combination comprising an antimicrobial and a resistance         inhibitor. Preferably, this combination comprises ceftriaxone at         a concentration of between 0.25 and 8 mg/l, preferably between 1         and 2.5 mg/l, and clavulanic acid at a concentration, of between         0.05 and 32 mg/l, preferably between 0.1 and 8 mg/l, and even         more preferably between 0.5 and 6 mg/l.

This medium is preferably used to distinguish:

-   -   a first group of E. coli HL Case bacteria;     -   a second group of KESC HL Case bacteria;     -   a third group of bacteria that are not resistant to         cephalosporins.

The invention also relates to a culture medium comprising:

-   -   a first substrate for detecting a beta-glucuronidase enzymatic         activity, preferably 6-chloro-3-indolyl-β-D-glucuronide, at a         concentration of between 25 and 750 mg/l, preferably between 40         and 300 mg/l, or a beta-galactosidase enzymatic activity,         preferably 5-bromo-6-chloro-3-indolyl-β-D-galactoside, at a         concentration between 25 and 500 mg/l, preferably between 40 and         150 mg/l;     -   a second substrate for detecting a beta-glucosidase activity,         preferably 5-bromo-4-chloro-3-indolyl-β-D-glucoside, at a         concentration of between 25 and 500 mg/l, preferably between 40         and 250 mg/l, or a tryptophanase or desaminase activity,         preferably tryptophan, at a concentration of between 50 and 5000         mg/l, preferably between 250 and 2000 mg/l;     -   two antimicrobials, which are preferably two antibiotics,         preferably cefpodoxime at a concentration of between 0.1 and 32         mg/l, preferably between 0.25 and 10 mg/l, and even more         preferably between 0.5 and 4 mg/l, and aztreonam at a         concentration of between 0.1 and 8 mg/l, preferably between 0.5         and 1.5 mg/l.

This medium is preferably used to distinguish:

-   -   a first group of E. coli ESBL or HL Case bacteria;     -   a second group of KESC ESBL or HL Case bacteria;     -   a third group of bacteria that are not resistant to         beta-lactamines and/or to cephalosporins.

The invention also relates to a culture medium comprising:

-   -   at least a first substrate for detecting alpha-glucoside         metabolism, preferably methyl-α-glucoside, at a concentration of         between 1 and 50 g/l, preferably between 5 and 20 g/l, or         5-bromo-4-chloro-3-indolyl-α-D-glucoside, at a concentration of         between 25 and 500 mg/l, preferably between 40 and 250 mg/l, or         5-bromo-4-chloro-3-indolyl-N-methyl-α-D-glucoside, at a         concentration of between 25 and 500 mg/l, preferably between 40         and 250 mg/l;     -   at least a second substrate for detecting a second activity         different than alpha-glucoside metabolism, preferably         5-bromo-4-chloro-3-indolyl-β-D-glucoside, at a concentration of         between 25 and 500 mg/l, preferably between 40 and 250 mg/l, or         6-chloro-3-indolyl-β-D-glucoside, at a concentration of between         25 and 500 mg/l, preferably between 40 and 250 mg/l, or         alizarine-β-D-galactoside, at a concentration of between 10 and         500 mg/l, preferably between 20 and 250 mg/l, or         5-bromo-6-chloro-3-indolyl-β-D-glucoside, at a concentration of         between 25 and 500 mg/l, preferably between 40 and 250 mg/l, or         5-bromo-6-chloro-3-indolyl-β-D-galactoside, at a concentration         of between 25 and 500 mg/l, preferably between 40 and 250 mg/l,         or 6-chloro-3-indolyl-β-D-galactoside, at a concentration of         between 25 and 500 mg/l, preferably between 40 and 250 mg/l.         Preferably, this second substrate makes it possible to detect a         beta-glucosidase or beta-galactosidase activity;     -   at least one antimicrobial, preferably an antibiotic, such as         vancomycin, at a concentration of between 0.5 and 128 mg/l,         preferably between 2 and 32 mg/l.

When the antibiotic is vancomycin, this medium is preferably used to distinguish:

-   -   a first group of vancomycin-resistant microorganisms, comprising         Enterococcus faecalis and Enterococcus faecium;     -   a second group of vancomycin-resistant microorganisms,         comprising Enterococcus casseliflavus and Enterococcus         gallinarum;     -   a third group of microorganisms that are not resistant to         vancomycin.

In this case, the first substrate is preferably methyl-α-glucoside, the second substrate is preferably 5-bromo-4-chloro-3-indolyl-β-D-glucoside or 6-chloro-3-indolyl-β-D-glucoside, and the antimicrobial is preferably vancomycin.

This medium is also preferably used to distinguish:

-   -   a first group of vancomycin-resistant microorganisms, comprising         Enterococcus faecalis;     -   a second group of vancomycin-resistant microorganisms,         comprising Enterococcus faecium;     -   a third group of microorganisms that are not resistant to         vancomycin or that express a natural resistance (E.         casseliflavus and E. gallinarum).

In this case, the first substrate is preferably 5-bromo-4-chloro-3-indolyl-N-methyl-α-D-glucoside or 5-bromo-4-chloro-3-indolyl-α-D-glucoside, the second substrate is preferably 6-chloro-3-indolyl-β-D-glucoside or alizarine-β-D-galactoside or 5 bromo-6-chloro-3-indolyl-β-D-glucoside or 5-bromo-6-chloro-3-indolyl-β-D-galactoside or 6-chloro-3-indolyl-β-D-galactoside, and the antimicrobial is preferably vancomycin.

This medium is also preferably used to distinguish:

-   -   a first group of vancomycin-resistant microorganisms, comprising         Enterococcus faecalis and Enterococcus faecium;     -   a second group of microorganisms, comprising Staphylococcus         aureus, that are intermediately resistant or resistant to         vancomycin;     -   a third group of microorganisms that are not resistant to         vancomycin.

In this case, the first substrate is preferably 5-bromo-4-chloro-3-indolyl-N-methyl-α-D-glucoside or 5-bromo-4-chloro-3-indolyl-α-D-glucoside, the second substrate is preferably 6-chloro-3-indolyl-β-D-glucoside or 5-bromo-6-chloro-3-indolyl-β-D-glucoside, and the antimicrobial is preferably vancomycin.

The table below makes it possible to distinguish the appropriate combinations of substrates and antimicrobial according to the species that it is desired to detect;

1st group of 2nd group of 3rd group of microorganisms microorganisms microorganisms 1st substrate 2nd substrate Antimicrobial E. faecalis and E. casseliflavus Microorganisms Methyl-α-glucoside 5-bromo- vancomycin E. faecium, and E. gallinarum, that are not 4-chloro- resistant to resistant to resistant to 3-indolyl- vancomycin vancomycin vancomycin β-D-glucoside or 6-chloro- 3-indolyl- β-D-glucoside E. faecalis, E. faecium, Microorganisms 5-bromo-4-chloro- 6-chloro- vancomycin resistant to resistant to that are not 3-indolyl-N-methyl- 3-indolyl- vancomycin vancomycin resistant to α-D-glucoside or β-D-glucoside or vancomycin or 5-bromo-4-chloro- alizarine- that express a 3-indolyl- β-D-galactoside natural resistance α-D-glucoside or 5-bromo- (E. casseliflavus 6-chloro-3- and E. gallinarum) indolyl-β- D-glucoside or 5-bromo-6- chloro-3-indolyl- β-D-galactoside or 6-chloro- 3-indolyl- β-D-galactoside E. faecalis and S. aureus, Microorganisms 5-bromo-4-chloro- 6-chloro- vancomycin E. faecium, resistant to that are not 3-indolyl-N-methyl- 3-indolyl- resistant to vancomycin resistant to α-D-glucoside or β-D-glucoside or vancomycin vancomycin 5-bromo-4-chloro- 5-bromo- 3-indolyl- 6-chloro-3- α-D-glucoside indolyl-β-D- glucoside

It may be relevant to also adjust the vancomycin concentration, preferably to between 0.5 and 12 mg/l.

The invention also relates to a culture medium comprising:

-   -   an antimicrobial, preferably an antibiotic such as cloxacillin;     -   a resistance mechanism inhibitor, such as preferably a         3rd-generation cephalosporin chosen from cefotaxime,         ceftazidime, cefpodoxime and ceftriaxone.

This medium is also preferably used to detect ESBL bacteria.

The second embodiment of the invention is not limited to distinguishing 3 groups of microorganisms, but can make it possible to distinguish 4, 5 or even more groups of microorganisms. It is then necessary to add, to the medium, markers for identification between the various groups.

In this respect, the invention also relates to a culture medium comprising:

-   -   a first substrate for detecting a beta-glucuronidase enzymatic         activity, preferably 6-chloro-3-indolyl-β-D-glucuronide, at a         concentration of between 25 and 750 mg/l, preferably between 40         and 300 mg/l, or a beta-galactosidase enzymatic activity,         preferably 5-bromo-6-chloro-3-indolyl-β-D-galactoside, at a         concentration of between 25 and 500 mg/l, preferably of between         40 and 150 mg/l;     -   a second substrate for detecting a beta-glucosidase, preferably         5-bromo-4-chloro-3-indolyl-β-D-glucoside, at a concentration of         between 25 and 500 mg/l, preferably between 40 and 250 mg/l;     -   a combination of antimicrobials, preferably a combination of         antibiotics such as         -   cefpodoxime at a concentration of between 0.5 and 32 mg/l,             preferably between 0.75 and 10 mg/l, and even more             preferably between 1 and 6 mg/l;         -   cloxacillin at a concentration of between 10 and 2000 mg/l,             preferably between 50 and 500 mg/l;         -   vancomycin at a concentration of between 0.5 and 128 mg/l,             preferably between 2 and 32 mg/l; and         -   amphoB at a concentration of between 0.5 and 64 mg/l,             preferably between 1 and 16 mg/l, even more preferably             between 1 and 8 mg/l;     -   a third substrate for detecting a desaminase activity, such as         histidine, phenylalanine, tryptophan or tyrosine, at a         concentration of between 50 and 5000 mg/l, preferably between         250 and 2000 mg/l.

This medium may also comprise a fifth antibiotic, which is cefsulodine, at a concentration of between 0.5 and 64 mg/l, preferably between 1 and 16 mg/l.

This medium is preferably used to distinguish:

-   -   a first group of E. coli ESBL bacteria;     -   a second group of KESC ESBL bacteria;     -   a third group of bacteria that are not resistant to         beta-lactamines and/or to cephalosporins;     -   a fourth group of Proteeae ESBL bacteria.

Similarly, the invention also relates to a culture medium comprising:

-   -   at least a first substrate for detecting alpha-glucoside         metabolism, preferably 5-bromo-4-chloro-3-indolyl-α-D-glucoside,         at a concentration of between 25 and 500 mg/l, preferably         between 40 and 250 mg/l, or         5-bromo-4-chloro-3-indolyl-N-methyl-α-D-glucoside, at a         concentration of between 25 and 500 mg/l, preferably between 40         and 250 mg/l;     -   at least a second substrate for detecting a second activity         different than alpha-glucoside metabolism, preferably         6-chloro-3-indolyl-β-D-glucoside, at a concentration of between         25 and 500 mg/l, preferably between 40 and 250 mg/l, or         6-chloro-3-indolyl-β-D-galactoside, at a concentration of         between 25 and 500 mg/l, preferably between 40 and 250 mg/l, or         alizarine-β-galactoside, at a concentration of between 10 and         500 mg/l, preferably between 20 and 250 mg/l, or         5-bromo-6-chloro-3-indolyl-β-D-glucoside, at a concentration of         between 25 and 500 mg/l, preferably between 40 and 250 mg/l, or         5-bromo-6-chloro-3-indolyl-β-D-galactoside, at a concentration         of between 25 and 500 mg/l, preferably between 40 and 250 mg/l,         or 6-chloro-3-indolyl-β-D-galactoside, at a concentration of         between 25 and 500 mg/l, preferably between 40 and 250 mg/l.         Preferably, this second substrate makes it possible to detect a         beta-glucosidase or beta-galactosidase activity;     -   a combination of antimicrobials, preferably a combination of         antibiotics such as         -   vancomycin at a concentration of between 0.5 and 128 mg/l,             preferably between 2 and 32 mg/l;         -   aztreonam at a concentration of between 1 and 150 mg/l,             preferably between 4 and 60 mg/l;         -   colistine at a concentration of between 1 and 100 mg/l,             preferably between 2 and 20 mg/l;         -   amphotericin B at a concentration of between 0.5 and 50             mg/l, preferably between 1 and 15 mg/l.

When one of the antibiotics is vancomycin, this medium is preferably used to distinguish:

-   -   a first group of vancomycin-resistant microorganisms, comprising         Enterococcus faecium,     -   a second group of vancomycin-resistant microorganisms,         comprising Enterococcus faecalis,     -   a third group of microorganisms that are not resistant to         vancomycin.

This medium is also preferably used to distinguish:

-   -   a first group of vancomycin-resistant microorganisms, comprising         Enterococcus faecium,     -   a second group of microorganisms, comprising Staphylococcus         aureus, that are intermediately resistant or resistant to         vancomycin;     -   a third group of microorganisms that are not resistant to         vancomycin.

The combinations of substrates according to the groups of microorganisms that it is desired to identify are presented, for example, in the table on page 21. By using an appropriate combination of antimicrobials, it is possible to distinguish not only three groups of microorganisms, but also 4, 5 or even more groups of microorganisms.

The invention also relates to the use of a combination of two culture media for distinguishing at least 3 groups of microorganisms in a biological sample, comprising:

-   -   a first group of microorganisms, belonging to a first species of         microorganisms and comprising a first mechanism of resistance to         a first treatment;     -   a second group of microorganisms, belonging to a species of         microorganisms that is identical to that of said first group of         microorganisms, but comprising a second mechanism of resistance         to a second treatment, different than that of said first group;     -   a third group of microorganisms that are not resistant to said         first and second treatment,

said combination of two culture media comprising:

-   -   a. at least a first substrate for detecting at least a first         enzymatic or metabolic activity of said first group of         microorganisms;     -   b. at least one marker for differentiating the first group of         microorganisms and the second group of microorganisms, said         marker being an inhibitor of the mechanism of resistance to the         first treatment and/or to the second treatment;     -   c. at least one antimicrobial that is active on said third group         of microorganisms.

This third embodiment of the invention makes it possible to distinguish, in the same sample, a first and a second group comprising the same species of microorganisms or the same taxon, each of the two groups being resistant to different treatments.

This embodiment of the embodiment thus makes it possible, for example, to distinguish, in the same sample, a first group comprising E. coli ESBL bacteria, and a second group comprising E. coli HL Case bacteria. In this specific case, the combination of two media may be the following:

-   -   at least a first substrate which makes it possible to         identify E. coli, for example a beta-glucuronidase substrate,         such as 6-chloro-3-indolyl-β-D-glucuronide, or a         beta-glucosidase substrate, such as         5-bromo-6-chloro-3-indolyl-β-D-galactoside;     -   a first identification marker which is a resistant mechanism         inhibitor, preferably cloxacillin;     -   a second identification marker which is another resistance         mechanism inhibitor, preferably clavulanic acid;     -   at least one antimicrobial which is cefpodoxime.

Reference is made to a combination of 2 media, i.e. a first medium may comprise:

-   -   a first substrate which makes it possible to identify E. coli,         which is 6-chloro-3-indolyl-β-D-glucuronide;     -   a first marker which is a resistance mechanism inhibitor,         preferably cloxacillin;     -   an antimicrobial, preferably an antibiotic, preferably         cefpodoxime,

while the second medium comprises:

-   -   a first substrate which makes it possible to identify E. coli,         such as 6-chloro-3-indolyl-β-D-glucuronide;     -   a second marker which is another resistance mechanism inhibitor,         preferably clavulanic acid;     -   an antimicrobial, preferably an antibiotic, preferably         cefpodoxime.

Another alternative would be to use a first medium comprising:

-   -   a first substrate which makes it possible to identify E. coli,         which is 5-bromo-6-chloro-3-indolyl-β-D-galactoside;     -   a first marker which is a substrate for a desaminase or for a         tryptophanase, preferably tryptophan;     -   an antimicrobial, preferably an antibiotic, preferably         cefpodoxime,

or the second medium comprises:

-   -   a first substrate which makes it possible to identify E. coli,         which is 6-chloro-3-indolyl-β-D-glucuronide;     -   a second marker which is a resistance mechanism inhibitor,         preferably clavulanic acid;     -   an antimicrobial, preferably an antibiotic, which is preferably         ceftazidime.

Those skilled in the art will choose each medium in such a way as to systematically obtain a combination according to the invention. The antimicrobial that is active on said third group is present in the two media. Those skilled in the art may in particular use a biplate, which makes it possible to readily compare the two media on which the same biological sample would have been deposited.

In this respect, the invention also relates to a biplate comprising a combination of two culture media, said combination comprising:

-   -   a. at least a first substrate for detecting at least a first         enzymatic or metabolic activity of said first group of         microorganisms;     -   b. at least one marker for differentiating the first group of         microorganisms and the second group of microorganisms, said         marker being an inhibitor of the mechanism of resistance to the         first treatment and/or to the second treatment;     -   c. at least one antimicrobial that is active on said third group         of microorganisms.

This third embodiment of the invention is not limited to distinguishing 3 groups of microorganisms, but may make it possible to distinguish 4, 5 or even more groups of microorganisms. It is then necessary to add additional identification markers to the medium, in order to discriminate the various groups.

In this respect, the invention relates to a biplate comprising a combination of two culture media, said combination comprising:

for the first medium,

-   -   a first substrate which makes it possible to identify E. coli,         for example a glucuronidase substrate, such as         6-chloro-3-indolyl-β-D-glucuronide, or a galactosidase         substrate, such as 5-bromo-6-chloro-3-indolyl-β-D-galactoside;     -   a second substrate which makes it possible to identify Proteeae,         for example a substrate for a desaminase or for a tryptophanase,         such as tryptophan;     -   a third substrate which makes it possible to identify the KESC         group, for example a glucosidase substrate, such as         5-bromo-4-chloro-3-indolyl-β-D-glucoside;     -   a marker for differentiating between ESBL strains and HL Case         strains, preferably a resistance inhibitor, preferably         clavulanic acid;     -   at least one antimicrobial which is preferably an antibiotic,         preferably ceftazidime;

for the second medium:

-   -   a first substrate which makes it possible to identify E. coli,         for example a glucuronidase substrate, such as in particular         6-chloro-3-indolyl-β-D-glucuronide, or a galactosidase         substrate, such as in particular         5-bromo-6-chloro-3-indolyl-β-D-galactoside;     -   a second substrate which makes it possible to identify Proteeae,         for example a substrate for a desaminase or for a tryptophanase,         such as tryptophan;     -   a third substrate which makes it possible to identify the KESC         group, for example a glucosidase substrate, such as in         particular 5-bromo-4-chloro-3-indolyl-β-D-glucoside;     -   at least one antimicrobial, preferably an antibiotic, preferably         ceftriaxone.

The examples below are given by way of explanation and are no way limiting in nature. They will make it possible to understand the invention more fully.

EXAMPLE

The example below is based on the phenotypic detection of ESBLs using the reduction of susceptibility of these strains to antibiotics and their sensitivity to combinations with β-lactamases inhibitors. For this, a biplate of CPS ID 3 base (chromogenic medium for detecting microorganisms in urine, and sold by bioMérieux under the reference 43541) with one half-agar containing an antibiotic and one half-agar containing an antibiotic/β-lactamases inhibitor combination was used.

1. Choice of Strains

In the context of the manipulations carried out, for evaluating the activity of the antibiotics active on gram-negative bacilli, various species of enterobacteria (Escherichia coli, Enterobacter aerogenes, Klebsiella pneumoniae, Serratia marcescens, Proteus mirabilis) and of nonfermenting gram-negative bacilli (Pseudomonas aeruginosa), capable of producing ESBLs, were used. ESBL-positive strains, high level cephalosporinase-producing strains (HL Case) and wild-type strains are compared in the trials.

For the manipulations regarding the antibiotics active on gram-positive bacteria, strains of gram-positive cocci (Staphylococcus aureus, Staphylococcus saprophyticus, Staphylococcus epidermidis, Enterococcus faecalis, Enterococcus faecium, Streptococcus agalactiae) and of gram-positive bacilli (Lactobacillus spp) were tested.

For the trials intended to evaluate the activity of the antifungals, various strains of yeasts (Candida albicans, Candida glabrata, Candida tropicalis, Candida krusei, Candida dubliniensis, Saccharomyces cerevisiae, Geotrichum capitatum) were used.

2. Preparation of Media

The medium used was a CPS ID3 medium (reference 43541) also comprising at least one antibiotic and at least one resistance mechanism inhibitor.

The composition of the media tested was the following:

Resistance Chromogenic substrate Antibiotic inhibitor Medium A 6-chloro-3-indolyl-β-D- Cefotaxime glucuronide 1 mg/l 5-bromo-4-chloro-3- indolyl-β-D-glucoside Tryptophan FeCl₃ Total: 1.73 g/l Medium B 6-chloro-3-indolyl-β-D- Ceftazidime 0.25 mg/l glucuronide 1.5 mg/l clavulanic acid 5-bromo-4-chloro-3-indolyl- β-D-glucoside Tryptophan FeCl₃ Total: 1.73 g/l

Osmosed water is added and the whole is homogenized and melted in a waterbath at 100° C. The base medium is dispensed into flasks, the number of which corresponds to the total number of media to be tested during the process. The flasks are then autoclaved for 15 min at 121° C. The media are brought back to and kept molten at 55±3° C. in a waterbath, in order to sterilely add the thermolabile additives (sterilized beforehand by filtration through 0.22 μm). The media are then poured into biplates 90 mm in diameter (i.e. approximately 9.5 ml/half-plate), and left on a flat surface so that they can set. The surface of the agars is then dried under a laminar flow hood for 30 min.

3. Inoculation of Media

An inoculum of 0.5 McF is prepared, in physiological saline, from 24-hour precultures at 36° C.±2° C. in an aerobic atmosphere on TSA medium, and then 1 μl of this suspension is transferred into 5 ml of physiological saline. In order to obtain a sufficient number of isolated colonies, a range of inocula made it possible to determine that the optimal amount of bacteria to be inoculated was from 10³ to 10⁴ CFU/ml. The inoculation is carried out directly on the two half-agars using a sterile swab. The cultures are then incubated at 37° C. in an aerobic atmosphere.

4. Reading of media: the readings are carried out at 18 hours (±30 min), 24 h (±1 h) and 48 h (±4 h). The density and the size of the colonies, and the appearance, the color and the coloration intensities of the mass and of the isolated colonies were observed, according to the following reading scales 1 to 3: 0: no growth; 0.1: trace of growth; 0.25: colonies of diameter<0.5 mm; 0.5: colonies of 0.5 mm in diameter; 0.75: 0.5 mm<diameter<1 mm; 1: colonies of 1 mm in diameter; 1.25: 1 mm<diameter<1.5 mm; 1.5: colonies 1.5 mm in diameter; 2: colonies 2 mm in diameter; 3: colonies of diameter>2 mm.

5. Results:

a) Screening of Antibiotics

The 5 antibiotics recommended by the NCCLS (National Committee for Clinical Laboratory Standards) were tested. For each product tested, a range was prepared in order to determine the concentrations that make it possible to inhibit the wild-type strains of the enterobacteria tested, without affecting the growth of the ESBL-positive strains or the HL Case-positive strains.

The concentrations selected are listed in table III hereinafter.

TABLE III Limiting values of the concentrations of antibiotics that allow inhibition of the wild-type strains of the enterobacteria tested, without affecting the growth of the ESBL-positive strains under the conditions tested Low value High value Cefotaxime 1 mg/l   2 mg/l Ceftazidime 2 mg/l 2.5 mg/l Ceftriaxone 1 mg/l 2.5 mg/l Cefpodoxime 2 mg/l  10 mg/l Aztreonam 1 mg/l 1.5 mg/l

The low value corresponds to the minimum concentration of the antibiotic required to inhibit the wild-type strains of the enterobacteria tested. The high value corresponds to the maximum concentration of the antibiotic that can be used without affecting the growth of the ESBL-positive strains tested.

At these concentrations, the separation of the wild-type and resistant strains is satisfactory, and the expression of the enzymatic activities on the CPS ID 3 medium is compliant.

In addition, it should be noted that ceftazidime is the only antibiotic tested and used in the detection of ESBLs which showed an activity on the wild-type strains of P. aeruginosa. A range was prepared in order to define the minimum concentration for complete inhibition of these strains, and the limiting value is 1.5 mg/l.

The addition of antibiotics had no effect on the expression of the bacterial enzymatic activities on the chromogenic medium. The groups of microorganisms were separated and identified both on control CPS ID 3 medium and on the media comprising the antibiotics as described above.

b) Screening of β-Lactamase Inhibitors

Three β-lactamases inhibitors (BLIs), i.e. clavulanic acid, tazobactam and sulbactam, were used. A range was prepared for each one, in the presence of cefotaxime, in order to determine the optimum concentration for inhibiting the ESBL-positive strains without impairing the growth of the HL Case strains.

Clavulanic acid appeared to be the most effective BLI in the presence of cefotaxime. Tazobactam and sulbactam required concentrations of greater than 2 mg/l in order to inhibit the ESBL-positive strains, whereas clavulanic acid was more active at much lower concentrations, over a broad operating range (from 0.1 to 8 mg/l when it is used in combination with cefotaxime).

Each antibiotic (cefotaxime, ceftazidime, ceftriaxone, cefpodoxime, aztreonam) was tested in the presence of a range of clavulanic acid in order to define the most effective combinations. The combinations selected are listed in table IV below.

TABLE IV Selected combinations of antibiotics and of clavulanic acid (CA) that inhibit the ESBL-positive enterobacterial strains tested, but allow the HL Case-positive strains to grow Cefotaxime 2 mg/l +CA  0.1 mg/l Ceftazidime 2.5 mg/l   +CA   2 mg/l Ceftriaxone 2 mg/l +CA 0.25 mg/l Cefpodoxime 9 mg/l +CA 0.25 mg/l Aztreonam 1 mg/l +CA  0.5 mg/l

The results obtained using a biplate containing the antibiotic alone on one side and the antibiotic+clavulanic acid combination on the other side are listed in table V.

TABLE V Antibiotic Antibiotic + alone clavulanic acid Wild-type E. coli ESBL-positive E. coli Pink colonies HL Case-positive E. coli Pink colonies Pink colonies Wild-type Proteeae ESBL-positive Proteeae Brown colonies HL Case-positive Proteeae Brown colonies Brown colonies Wild-type KESC ESBL-positive KESC Green colonies HL Case-positive KESC Green colonies Green colonies

The addition of β-lactamase inhibitors had no effect on the expression of the bacterial enzymatic activities on the chromogenic medium. The groups of microorganisms were separated and identified both on control CPS ID 3 medium and on the media comprising β-lactamase inhibitors.

c) Combination of Antibiotics

Given the relative activities of the antibiotics and of clavulanic acid, the following were combined:

-   -   cefotaxime (antibiotic active on ESBL-positive strains in         combination with the lowest concentration of clavulanic acid),     -   ceftazidime (antibiotic active on wild-type strains of P.         aeruginosa), and     -   clavulanic acid,

so as to be able to inhibit, firstly, the wild-type strains (including those of pyocyanic bacillus), and the ESBL-positive strains of the enterobacteria tested by the addition of the BIL.

Such a combination was tested on strains of P. aeruginosa; this species is naturally resistant to cefotaxime but sensitive to ceftazidime. When 1.5 mg/l of CAZ (ceftazidime), 1 mg/l of CTX (cefotaxime) and 0.25 mg/l of CA (clavulanic acid) were combined, all the wild-type strains and the ESBL-positive strains of the enterobacteria tested were inhibited and only the collection of HL Case strains and the ESBL-positive P aeruginosa strains grew. It involves a biplate with CAZ alone on one side and CTX plus clavulanic acid on the other.

The addition of these combinations of antibiotics had no effect on the expression of the bacterial enzymatic activities on the chromogenic medium. The groups of microorganisms were separated and identified both on control CPS ID 3 medium and on the media comprising such combinations of antibiotics.

d). Dye Assay

A medium according to the invention was also employed for use in a biplate, one of the sides containing an antibiotic, and the second containing another antibiotic or a combination of antibiotics. Given that the same CPS ID 3 medium base is used on either side, these two sides were differentiated by the presence of a dye.

The dye tested, Evans blue, gives the medium a green color. The coloration has made it possible to readily differentiate the 2 sides of the biplate without affecting the fertility of the medium, or impairing the reading of the enzymatic activities of the colonies. After having produced a range of Evans blue, added before or after autoclaving, the values selected were the following:

-   -   1.5 or 2 mg/l if the dye is added after autoclaving.     -   between 2 and 5 mg/l if it is added before autoclaving.

e). Inhibition of Gram-Positive Bacteria

ESBLs are a mechanism of resistance to β-lactamines that is found only in gram-negative bacilli; it is therefore advisable to inhibit the gram-positive bacteria via the medium. Two antibiotics, linezolide and vancomycin, were used in the medium according to the invention for the purpose of inhibiting the sensitive gram-positive bacteria.

For vancomycin, under the conditions tested, a concentration between 2 and 32 mg/l, and in particular 2 to 5 mg/l, makes it possible to inhibit the sensitive grain-positive bacteria without interfering with the detection of the ESBL bacteria.

For linezolide, under the conditions tested, a concentration between 2 and 64 mg/l, and in particular 4 to 16 mg/l, makes it possible to inhibit the sensitive gram-positive bacteria without interfering with the detection of the ESBL bacteria.

The inhibition of the gram-positive bacteria made it possible to improve the detection of the ESBL bacteria in polymicrobial samples and the specificity of their coloration.

f) Inhibition of Yeasts

A medium according to the invention can also comprise antifungals in order to inhibit the possible presence of yeasts which could grow on the medium and which could impair microorganism growth.

Two antifungals were therefore tested: voriconazole and amphotericin B.

For amphotericin B, under the conditions tested, a concentration between 1 and 32 mg/l, and in particular 2 to 8 mg/l, makes it possible to inhibit the sensitive yeasts without interfering with the detection of the ESBL bacteria.

For voriconazole, under the conditions tested, a concentration of between 1 and 64 mg/l, and in particular 4 to 16 mg/l, makes it possible to inhibit the sensitive gram-positive bacteria without interfering with the detection of the ESBL bacteria.

The inhibition of the yeasts made it possible to improve the detection of ESBL bacteria in polymicrobial samples and the specificity of their coloration.

6. Conclusion

These results demonstrate that the medium according to the invention makes it possible to isolate and apparently identify ESBL-producing bacteria, differentiating them from high level cephalosporinase-producing strains. The use of a biplate containing a cephalosporine alone on one side and a cephalosporine/clavulanic acid combination on the other, in a CPS ID 3 base, is particularly advantageous.

Example 2

This second example is based on the phenotypic detection of ESBLs using the reduction of susceptibility to antibiotics and the sensitivity of HL Cases to combinations with tobramycin or cloxacillin or dicloxacillin, and presents the use of a cephalosporine mentioned above (CTX, CAZ, CPD, CRO, ATM) in combination with a compound that inhibits cephalosporinases (cloxacillin, dicloxacillin and tobramycin). Such a medium makes it possible to inhibit bacteria which have a “natural” cephalosporinase, most of those which have only a high level cephalosporinase (HL Case), while at the same time allowing growth of ESBL bacteria.

1. Choice of Strains

In the context of the manipulations carried out, for evaluating the activity of antibiotics that are active on gram-negative bacilli, various species of enterobacteria (Escherichia coli, Enterobacter aerogenes, Klebsiella pneumoniae, Proteus mirabilis) and of nonfermenting gram-active bacilli (Pseudomonas aeruginosa) capable of producing ESBLs, were used. In the assays, ESBL-positive strains, strains producing high level cephalosporinase (HL Case) and wild-type strains are compared.

2. Preparation of the Medium

The medium used was a CPS 1D3 medium (43541), also comprising:

-   -   ceftazidime at 2.5 mg/l and tobramycin at 2 mg/l (medium A) or     -   ceftriaxone at 2 mg/l and cloxacillin at 150 mg/l (medium B) or     -   cefpodoxime at 2 mg/l and dicloxacillin at a concentration of         between 500 and 1000 mg/l (medium C).

Osmosed water is added and the whole is homogenized and melted in a waterbath at 100° C. The basic medium is dispensed into flasks, the number of which corresponds to the total number of media to be tested during the process. The flasks are then autoclaved for 15 min at 121° C. The media are brought back to and kept molten at 55±3° C. in a waterbath, in order to sterilely add the thermolabile additives (sterilized beforehand by filtration through 0.22 μm). The media are then poured into plates 35 mm in diameter and left on a flat surface so that they can set. The surface of the agars is then dried under a laminar flow hood for 30 min.

3. Inoculation of Media

This step is carried out as described in example 1.

4. Reading of Media

This step is carried out as described in example 1

5. Results:

Medium A comprising ceftazidime and tobramycin made it possible to inhibit all the wild-type strains and all the HL Cases tested. Only the ESBL-positive strains were detected on this medium.

Medium B comprising ceftriaxone and cloxacillin made it possible to inhibit all the HL Cases and all the wild-type strains except HL Case and wild-type P aeruginosa, and grew only the majority of the ESBL-positive strains.

Medium C comprising cefpodoxime and di-cloxacillin made it possible to inhibit all the wild-type strains and the majority of the HL Cases, without affecting the growth of ESBL-positive strains.

Example 3

This third example is based on the phenotypic detection of enterococci resistant to glycopeptides, with specific distinction of Enterococcus faecalis and E. faecium, using the reduction of susceptibility to antibiotics and the demonstration of an enzymatic activity: β-glucosidase, and of a metabolic activity: Methyl-α-glucoside acidification.

1. Choice of Strains

In the context of the manipulations carried out, for evaluating the activity of the antibiotics active on enterococci, various species of Enterococcus (Enterococccus faecalis, Enterococcus faecium, Enterococcus casseliflavus, Enterococcus gallinarum,) were used. In the assays, strains resistant to glycopeptides (VRE) and wild-type strains are compared.

2. Preparation of the Medium

The medium used was a Columbia medium (51026), also comprising:

-   -   5-bromo-4-chloro-3-indolyl-β-D-glucopyranoside (X-Glu) at 100         mg/l,     -   methyl-α-D-glucoside at 9 g/l,     -   neutral red at 25 mg/l,     -   bilial salts at 5 g/l,     -   vancomycin at 4 mg/l,     -   amphotericin B at 2 mg/l.

Osmosed water is added and the whole is homogenized and melted in a waterbath at 100° C. The basic medium is dispensed into flasks, the number of which corresponds to the total number of media to be tested during the process. The flasks are then autoclaved for 15 min at 121° C. The media are brought back to and kept molten at 55±3° C. in a waterbath, in order to sterilely add the thermolabile additives (sterilized beforehand by filtration through 0.22 μm).

The media are then poured into plates 90 mm in diameter and left on a flat surface so that they can set. The surface of the agars is then dried under a laminar flow hood for 30 min.

3. Inoculation of Media

This step is carried out as described in example 1.

4. Reading of Media

This step is carried out as described in example 1.

5. Results:

On this medium, only the glycopeptide-resistant enterococcal strains develop and form colonies.

The resistant E. faecalis and E. faecium strains form green colonies, whereas those of E. casseliflavus and of E. gallinarum form blue-to-violet colonies.

This medium therefore makes it possible to differentiate these two groups of enterococci and to provide a suitable therapeutic response.

Example 4

This fourth example is based on the phenotypic detection of glycopeptide-resistant enterococci, with specific distinction of Enterococcus faecalis and E. faecium, using the reduction of susceptibility to antibiotics and the demonstration of two enzymatic activities: α-glucosidase and β-galactosidase or β-glucosidase.

1. Choice of Strains

In the context of the manipulations carried out, for evaluating the activity of antibiotics active on enterococci, various species of Enterococcus (Enterococccus faecalis, Enterococcus faecium, Enterococcus casseliflavus, Enterococcus gallinarum) were used. In the assays, strains resistant to glycopeptides (VRE) and wild-type strains are compared.

2. Preparation of the Medium

The media used were a Columbia medium (51026), also comprising:

-   -   5-bromo-4-chloro-3-indolyl-N-methyl-α-D-glucopyranoside         (GreenA-α-Glu) at 150 mg/l,     -   6-chloro-3-indolyl-β-glucopyranoside (Rose-b-Glu [Pink-b-Glu])         at 200 mg/l, or:     -   5-bromo-4-chloro-3-indolyl-N-methyl-α-D-glucopyranoside         (GreenA-α-Glu) at 150 mg/l,     -   alizarine-β-galactopyranoside at 50 mg/l

and vancomycin at 8 mg/l,

an amphotericin B at 4 mg/l,

and colistine at 2 mg/l,

and aztreonam at 32 mg/l.

Osmosed water is added and the whole is homogenized and melted in a waterbath at 100° C. The two basic media are dispensed into flasks. The flasks are then autoclaved for 15 min at 121° C. The media are brought back to and kept molten at 55±3° C. in a waterbath, in order to sterilely add the thermolabile additives (sterilized beforehand by filtration through 0.22 μm). The media are then poured into plates 90 mm in diameter and left on a flat surface so that they can set. The surface of the agars is then dried under a laminar flow hood for 30 min.

3. Inoculation of Media

This step is carried out as described in example 1.

4. Reading of Media

This step is carried out as described in example 1.

5. Results:

On the medium containing a substrate for a-glucosidase and for β-glucosidase, the resistant E. faecium strains form violet colonies, whereas the resistant E. faecalis strains form pink colonies. The E. casseliflavus and E. gallinarum strains (natural resistances) are inhibited due to the concentration of vancomycin.

This medium therefore makes it possible to differentiate these two groups of enterococci and to provide a suitable therapeutic response and also a follow-up of the local epidemiology.

On the medium containing a substrate for a-glucosidase and for β-galactosidase, the resistant E. faecium strains form violet colonies, whereas the resistant E. faecalis strains form green colonies. The E. casseliflavus and E. gallinarum strains (natural resistances) are inhibited due to the concentration of vancomycin.

This medium therefore makes it possible to differentiate these two groups of enterococci and to provide a suitable therapeutic response and a follow-up of the local epidemiology. 

1. A method for distinguishing among at least three groups of microorganisms that may be present in a biological sample, the at least three groups comprising: a first group of microorganisms belonging to a first taxon of Gram negative bacteria, the first group of bacteria exhibiting a mechanism of resistance to a treatment; a second group of microorganisms belonging to a second taxon of Gram negative bacteria, the second taxon of bacteria being different than said first taxon, and exhibiting a mechanism of resistance to a treatment identical to the mechanism of the first group; and a third group of Gram negative bacteria that is not resistant to said treatment, the method comprising: inoculating a culture medium with the biological sample, wherein the culture medium comprises: a first substrate for detecting a first enzymatic or metabolic activity of said first group of microorganisms; a marker for differentiating the first group of microorganisms and the second group of microorganisms, said marker being a substrate for detecting an enzymatic or metabolic activity of said second group of microorganisms; and an antimicrobial that is active on the third group of microorganisms; and distinguishing among any members of the three groups of microorganisms that are present on the culture medium to determine of which group of microorganisms they are members on the basis of their interactions with the first substrate, the markers, and the antimicrobial.
 2. The method according to claim 1, wherein: the first group of microorganisms is selected from E. coli ESBL and HL Case bacteria; and the second group of microorganisms is selected from KESC ESBL or HL Case bacteria.
 3. The method of claim 1, wherein: the third group of microorganisms is bacteria not resistant to beta-lactamines and/or cephalosporins.
 4. The method of claim 1, wherein: the first group of microorganisms is E. coli ESBL bacteria; the second group of microorganisms is KESC ESBL bacteria; and the third group of microorganisms is bacteria not resistant to beta-lactamines.
 5. The method of claim 1, wherein: the first group of microorganisms is E. coli HL Case bacteria; the second group of microorganisms is KESC HL Case bacteria; and the third group of microorganisms is bacteria not resistant to cephalosporins.
 6. The method of claim 1, wherein: the first group of microorganisms is E. coli ESBL bacteria; the second group of microorganisms is KESC ESBL bacteria; the third group of microorganisms is bacteria not resistant to beta-lactamines and/or cephalosporins; and the biological sample further comprises a fourth group of microorganisms that is Proteeae ESBL bacteria.
 7. The method of claim 1, wherein: the first substrate is a substrate for detecting a beta-glucuronidase or beta-galactosidase enzymatic activity; the marker is a second substrate for detecting a beta-glucosidase, tryptophanase, or desaminase activity; and the antimicrobial is ceftazidime.
 8. The method of claim 1, wherein: the first substrate is a substrate for detecting a beta-glucuronidase or beta-galactosidase enzymatic activity; the marker is a second substrate for detecting a beta-glucosidase, tryptophanase or desaminase activity; and the antimicrobial is cefpodoxime and cloxacillin.
 9. The method of claim 1, wherein: the substrate is a first substrate for detecting a beta-glucuronidase or beta-galactosidase enzymatic activity; the marker is a second substrate for detecting a beta-glucosidase, desaminase or tryptophanase activity; and the antimicrobial is ceftriaxone and clavulanic acid.
 10. The method of claim 1, wherein: the substrate is a first substrate for detecting a beta-glucuronidase or beta-galactosidase enzymatic activity; the marker is a second substrate for detecting a beta-glucosidase activity; the antimicrobial is a combination comprising: cefpodoxime, cloxacillin, vancomycin, and amphotericin B; and the culture medium further comprises a third substrate for detecting a desaminase activity.
 11. The method of claim 10, wherein the antimicrobial further comprises cefsulodine.
 12. The method of claim 1, wherein: the first group of microorganisms is E. coli ESBL bacteria; the second group of microorganisms is KESC ESBL bacteria; the third group of microorganisms is bacteria not resistant to beta-lactamines and/or to cephalosporins; the biological sample further comprises a fourth group of microorganisms that is Proteeae ESBL bacteria; the first substrate is a substrate for detecting a beta-glucuronidase or beta-galactosidase enzymatic activity; the marker is a second substrate for detecting a beta-glucosidase activity; the antimicrobial is a combination comprising: cefpodoxime, cloxacillin, vancomycin, and amphotericin B; and the culture medium further comprises a third substrate for detecting a desaminase activity.
 13. The method of claim 1, wherein: the first group of microorganisms is E. coli ESBL bacteria; the second group of microorganisms is KESC ESBL bacteria; the third group of microorganisms is bacteria not resistant to beta-lactamines and/or to cephalosporins; the biological sample further comprises a fourth group of microorganisms that is Proteeae ESBL bacteria; the first substrate is a substrate for detecting a beta-glucuronidase or beta-galactosidase enzymatic activity; the marker is a second substrate for detecting a beta-glucosidase activity; the antimicrobial is a combination comprising: cefpodoxime, cloxacillin, vancomycin, amphotericin B, and cefsulodine; and the culture medium further comprises a third substrate for detecting a desaminase activity. 